09 Suitability for Common Uses

Pumice Deposits of the Klamath Indian Reservation, Klamath County, Oregon

Suitability for Common Uses

Tests of the physical and chemical properties of pumice from the Klamath Reservation by the writer and by the Bureau of Reclamation laboratories, as well as data obtained from the reports by Moore (1937) and Williams (1942), indicate that the pumice is suitable, with some limitations, for use as an aggregate and as an abrasive. Only preliminary tests were made on the pumice for its suitability as a pozzuolanic material, because the cost of such testing is very high and not warranted until such time as a demand for large tonnages for pozzuolana can be foreseen.

In a report by R. H. Cook (1951) of the Bureau of Reclamation on the properties of three samples of the pumice for the Reservation, he states:

“From a petrographic standpoint the pumice fragments constituting the three samples appear to have potential value for use as aggregate in lightweight concrete. However, samples No. 56 and 59 (Pumice flow material–see table 2) contain excessive amounts of fine material and sample No. 58 (Pumice fall material–see table 2) is deficient in several size fractions. Inasmuch as grading is a critical factor in producing a workable lightweight concrete, this poor graduation might impose economic restrictions on use of the material as aggregate because of the large volume of material which must be processed to produce an aggregate of proper grading.

“Experience indicates that concrete made of excessively fine pumice is generally of poor quality and suited for only very limited use. Excessive absorption of pumice tends to reduce workability of concrete. Heat treatment of the pumice tends to overcome this difficulty, and in addition tends to increase the quality of concrete which can be made. The glass of which the pumice and fine ash are composed is a type known to be deleteriously reactive with high-alkali cement. “

In the same report he also evaluates the pumice for its suitability for pozzuolana. His comments are as follows:

“From a petrographic standpoint, the samples appear worthy of further testing for suitability as pozzolan, inasmuch as experience indicates that some dacite tuffs and ashes produce effective pozzolans. All these samples would require grinding to achieve the fineness necessary for pozzolanic materials, consequently, cost of processing may decide the feasibility of commercial exploitation. The rock and mineral particles present would tend to reduce the pozzolanic activity of the samples. However, it cannot be determined without further testing whether the amounts of these inactive constituents are so great as to render the material unusable. “

Tests by the author show similar properties for a number of other samples of both the pumice fall and the pumice flow, though two samples from the pumice flow deposits were even more absorptive than those examined by the Bureau of Reclamation. The high degree of interconnection of voids (effective permeability) in the flow pumice reduces the thermal and acoustic insulating values of the pumice, and when used in concrete causes excessive absorption of water. This reduces the workability of the concrete.

Tests have shown that pumice in the fall deposits meets most requirements for use as a lightweight aggregate. Apparently it is sufficinetly inert, and material can be obtained that is pure and largely free of contaminating substances. Individual pumice fragments are light in weight, and have adequate structural strength. It is deficient in that the range in the size of particles is small, consisting almost entirely of coarse sand-sized grains. The pumice of the flow deposits is equally inert, and locally, pure and unadulterated pumice can be obtained. The material contains a wider distribution in the size of fragments than the pumice flow, but in most localities it contains too high a proportion of fine particles or too many large lumps to be used without processing. The large lumps of pumice are extremely frothy, a condition which decreases their strength and increases their absorptive characteristics. Nevertheless, the pumice fall material that has been tested is much the same as that being utilized for aggregate and plaster sand to the north of the Reservation. The deposits to the north, however, have a slight advantage in being better sorted and requiring less crushing and screening to meet the specifications of the consumers.

Tests of the pumice on the Reservation show that neither the flow nor fall pumice is suitable for high-quality abrasive, because it is uniform in neither texture nor vesicle size, and it has a fairly high content of phenocrysts and foreign mineral grains. A much lower grade abrasive can be obtained, however, by hand sorting lump pumice from the flow deposits, but at the present time there apparently is little demand for such material.